480 USES OF WOOD PULP. 



the square inch, and this is regarded the proper limit. If the pressure shows a 

 tendency to exceed this, the heat is shut off and a valve opened which permits the 

 sulphurous gases to escape into the sulphite tank, where they are condensed and 

 the chemical principle saved. During the whole boiling process samples of the 

 liquid are withdrawn from the boiler and tested, so that the attendant keeps exact 

 trace of the progress of the chemical action going on within. These tests are made 

 by mixing in a test tube a known quantity of the bisulphite liquid with a certain 

 proportion of ammonia and noting the quantity of normal sulphite of lime that is 

 precipitated. 



The exact nature of the chemical reaction which takes place between the bisul- 

 phite and the increasing elements of the wood is highly interesting from a scien- 

 tific standpoint, but is too technical and withal too vaguely determined to come 

 properly within the scope of this report. When the boiling is finished, the valve 

 leading to the sulphite tank is opened and the gases withdrawn and condensed 

 therein until the pressure is reduced to nearly the atmospheric limit, when the 

 waste sulphite or "lye" is drawn off from the bottom of the boiler, to be used in 

 the digesting stage of the next charge. The manholes are then opened and a flood 

 of water poured in, which washes the softened, pulpy wood out into receiving tanks, 

 where it is washed and stirred in fresh water until the free sulphite is eliminated. 



Thence it is passed in a stream of water under a gang of stamps, similar to a 

 quartz stamp mill, which macerates it to a coarse white pulp, and passes on through 

 a series of rotary mixers, and, in the manufacture of cellulose, is run out in an 

 endless web, like ordinary paper. This is about the thickness of medium paste- 

 board, and is either cut into sheets or wound into rolls of about 50 kilograms in 

 weight for packing. When exported as pulp, it is air dried and packed in bales 

 of about 200 pounds in weight. 



At every stage of the process after the softened wood comes from the boiler, the 

 utmost care is taken to purify it from every blemish and impurity. Small specks 

 and fragments of knots are picked out of the pulp as it flows through the various 

 machines. A keen-eyed operative stands where the cellulose web is reeled out 

 from between the final pair of steam-heated rollers and with a sharp knife deftly 

 stabs and removes each passing blemish, and in the packing room each sheet and 

 roll is carefully examined inch by inch and the tiniest speck that would mar the 

 whiteness and purity of the material is eliminated. In one factory at Aschaffen- 

 burg forty workmen are thus employed, besides forty more who examine and pre- 

 pare the wood before it enters the mill. It is this extraordinary care in inspecting 

 the raw material and finished product which gives to the German cellulose its supe- 

 riority and enables it to hold its place in foreign markets in competition with the 

 cheaper qualities of local manufacture. It is said to be the lack of sufficient skilled 

 operatives and the high wages that such labor commands in the United States that 

 have hitherto constituted the principal advantages of the German pulp makers in 

 maintaining their American trade against home competition. Another point in their 

 favor is the fact that American pine is more resinous than the German, and not 

 only requires longer treatment, but loses more of its substance, while producing 

 less fiber from a given amount of wood. 



It remains to speak briefly of the most important of the auxiliary processes in- 

 volved that of preparing the liquid bisulphite of lime, which is the principal agent 

 used in the digesting and boiling operations above described. For this there are 

 several methods, the two principal of which are (i) the passing of sulphurous acid 

 gases, obtained by burning crude sulphur or pyrites in open-air kilns, through a 

 weak milk of lime, and (2) by exposing wet limestone or dolomite (a native double 

 carbonate of lime and magnesia) to the action of sulphurous acid gases. The latter 

 method was perfected by Dr. Mitscherlich, who ranged the lumps of limestone and 



